text:
Is starting a jet engine without ground support possible?
We have had more... than... one question about jet aircraft taxiing about the airport without their jet engines running. Those address several issues such as cost vs savings and regulatory approval.
My question assumes that an in-wheel electric motor, tug or even pull-chain based solution has been developed, certified, deemed cost-effective and installed.
Let's say that I am now sitting on the taxi-way and am 5th in line for take off. It's time to fire up those jets so they can warm up and we can get the beast into the air. According to this question about how turbine engines are started, it appears that I'm going to need some sort of ground-based support to get the N2 stage spinning. That question indicates that a couple of early, WWII era, jet engines had a built in motor that could get the turbines spinning fast enough for a start, but it seems to me that any modern commercial air-carrier grade engine will need some sort of external help to fire up. I suppose if there was a tug that had pulled me to this point, it could have the support infrastructure built in to get the turbines spinning, but any sort of self- (or ground-) propelled system would seem to lack that.
Now that we're nowhere near the terminal, how the heck are we going to start the engines?
I realize that this question is somewhat speculative in nature, but I believe it could be answered based on some existing or in-development ability (that I'm not aware of) to start an engine without ground support. It could also be my misunderstanding that ground support is not required to start a modern commercial aircraft engine (GE90, RR Trent series, LEAP etc.)

I think this premise: "but it seems to me that any modern commercial air-carrier grade engine will need some sort of external help to fire up" is false. While its not unheard of for an aircraft to have an inop APU, its unlikely that it would leave the gate without a started engine for cross-bleed air if thats the case. I've flown many times where the engines weren't started until after push-back without any ground assist...

See Auxiliary Power Unit

Wow. I look back at this question 4 years later and... I've learned so much since then.

use battery to start APU. use APU power and air to start engine. Use that engine to start rest of engines. Easy, but slow.

Modern jet transport category aircraft have APUs and they will be running if no engines are.  Batteries on jets do not work very long with all electrical buses energized and the first thing you do after turning the batteries on is seeing that they are working correctly and then starting the APU (assuming no GPU is hooked up, if there is a GPU then starting the APU will be deferred until just before the GPU is disconnected).
Thus, any aircraft on a theoretical no-engine taxi to the runway will have a running APU providing electricity to run the airplane and bleed air for an attempt at air conditioning (some aircraft are better at this then others).  When it is time to start the engines they can be started using the APU as the bleed air source and this is a normal method of starting and no different than the method used currently when the plane leaves the gate (and for some airplanes they only start one engine and taxi on that as long as possible before starting the other engine).
As long as the plane has a running APU, it can complete a normal engine start with no ground assistance.  The only limitation will be turbine warm up time, which just means you'll need to make sure the engines are started a few minutes before takeoff thrust is applied.
Just an aside, but currently the only ground support strictly required is a tug to push the airplane away from the gate and someone to operate the jetbridge.  Aircraft and engine startup is self-contained unless the APU is inoperative.

One thing that you don't cover is that some jet engines (particularly smaller ones) use electric starters and therefore don't need air to start at all. In fact, they typically are started from the batteries.

If GPU is used, how much power (amps, kilowatts) will be needed to start a commercial airliner eg. A380, 747, 767, etc?

This depends on the aircraft.
Most large jet aircraft are equipped with an APU (Auxiliary Power Unit). This is a small turbine power source usually in the back of the plane that can be started using only the onboard batteries. Once started the APU can provide electrical power as well as bleed air to start the engines.
Not all planes (but most modern ones) have an APU to provide bleed air and some require a ground based source of air pressure to start up, generally the airport has mobile units for this.
Piston planes (although not many are flown commercially any more), can generally be started by their internal batteries. If you are lucky enough to be in a piston plane form the 30's or 40's you may encounter a Coffman Starter which basically uses a blank shotgun shell to generate pressure in the cylinder and turn the engine over.
Small turbo props often have turbines small enough to be started by an electric starter. This extends to some small jets as well.
If a plane is out on the ramp and for what ever reason the batteries are dead or they die trying to start the APU, most airports have portable Ground Power Units that they can bring out to the plane for starting and providing power.

If you noticed, he just asked about jet aircraft on the taxiway waiting to take-off.

I was answering in the spirit of the title question but you are correct there was no need to cover non jet aircraft, i was simply offering it for comparison.

If the plane is a turboprop, it's possible to start the engines without using the APU. It's called a "buddy start". Two planes are parked nose to nose, one with engines running, the props are reversed and engine power is increased. On the non running craft, the props are set to windmill as the airblast hits them. Probably in a multi engine plane, only I engine will be started, and the others feathered until the first engine is running.
This is done on occasion in the military, when the APU of the non running aircraft is down. It probably isn't allowed on a commercial plane.

While not used for commercial aircraft, many military aircraft used started cartridges. These were slow burning explosives much like black powder packed into a canister and installed in the side of the engine. When ignited they produced a relatively high speed exhaust that rotate the turbines to reach starting speeds.
They were used regularly on alert B-52 and KC135 aircraft during the cold war.

Others have noted that the APU is the normal means of engine start.  I would like to note the extreme undesirability of your proposed scheme.  Airlines live and die on despatch reliability and OTP, On Time Performance.  Instead of performing engine start at a place easily accessible to maintainers, you want to do it shortly before take-off.  This not only leaves no slack time to deal with MEL items that may only be encountered after engine start, or even a failure to start, it leaves the aircraft far away from where these matters may be dealt with.  Worse still, it greatly increases the time pressure on pilots.
Most undesirable.
It would seem a very good way to turn a minor MEL item from no delay into an hour or more of delay.
It turns many common minor squawks into ground turn-backs instead of an on-time departure.  I'm sorry, but it is a bad idea, from safety and passenger satisfaction perspectives too.  It means that you have loaded pax and taken them around the airport and guaranteed significant delays to their travel if a problem arises during engine start and post-start checks - with a normal departure sequence, if problems arise before push back, you may be able to transfer loads to a spare aircraft and still achieve an on time departure (defined as within 15 minutes of scheduled departure)  even if you can't do that, you may still get them to their destination on time by electing to increase fuel burn to increase speed.  This is quickest on services without meals.
Whilst all airlines are very conscious of fuel usage, this scheme has little potential to save fuel, whilst imposing tremendous operational difficulties on the operator that do no one any good.
To get back to your question, as well as cartridge starters, there were in the past a number of turbine based starters using such propellants as 'AVPIN' for military aircraft, whilst today, there are still ground gas generator units (turbines with oversized compressor sections) that may be used to start aircraft with an unservicable APU and buddy start hoses which may be used to rescue aircraft stranded due to an unservicable APU at a port without ground support equipment.  Also, some military aircraft use small gas turbines such as the Solar T-65 as starter engines (rather than using bleed air from a small turbine).

Single engine taxi is a common practice. Isn't that in conflict with your first paragraph?

Well, so someone said.  It isn't very common on departure in my experience.  I have in the past asked Flight Ops to encourage an engine shutdown on post-flight taxi, in preference to operating with one reverser deployed - mainly because doing that sets 'dolls eyes' for a reverser fault that then requires expensive investigation when nothing is actually wrong.

In most cases, single engine taxi after push back would be a violation of the FCOM procedures, but different countries and airlines may operate differently.  It's a dumb thing to do.  The check list says 'start engines', after all...

Ok, I understand that single engine taxi out is controversial. EZY seems to do it. Some recommend it for taxi out not shorter than 7'. Others don't do it for the exact reasons that you mentioned. I am not an airline pilot - just curious.

Okay, I know what an APU is, but what is an U/S APU?

U/S = Unservicable, it isn't working.

Not sure how I never noticed this answer until now. This question was specifically framed to ignore the usefulness of starting the engines on the taxiway near the departure end of the runway and, instead, to focus on how that could be done. In reality, only the last paragraph of your answer addresses the actual question.

Most of the time, the APU of the aircraft is kept running when the airplane is on the ground to provide the bleed air and electrical power to start up the main engines. As it happens, the APU does not need bleed air to start up so if you are starting the airplane up after leaving it, say overnight, you can start the APU up first and then start up the rest of the engines and voilà, you can take-off now. That is how it works on jet aircraft so no one gets stuck in an airport in the middle of nowhere.

Not a problem in most aircraft.  Smaller jet engines like Williams jet engines used on light business jets eg Phenom 300, etc would use an electric start.  If one engine was already running and the Starter Generator was running, it's an easy matter to motor the other engine off ship's electrical power.
Larger engines which used air turbine starters can be powered up a couple of ways.  You can use an APU, as suggested above, but the easiest way is just to use a bleed air crossfeed from an operating engine to spin up the other engine.
Pyrotechnic cartridge starters are common on a number of military aircraft for starting engines or APUs in the field.  It's a simple, disposable solution, but a little dirty and only one shot.  Other solutions are hydraulic pressure reservoirs used to crank up APUs, similar to the system employed on the F-16 to start up it's dedicated engine APU called a Jet Fuel Starter (JFS).

Thanks. I'm not sure what your answer added that hadn't already been addressed in most of the other answers.


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Is it bad for the engine to perform a touch & go?
I just watched a video about the traffic pattern. In the comment section below, the uploader spoke about touch & go's:

I don't like to do touch and go's, as a student pilot I used to do them cause you saved money, but its not worth it. Always better to get off the runway, let the engine stabilize**, and then set up properly for the next flight/takeoff.
** by stabilize I mean let the engine warm up under its own power on the ground, because the engine was just at idle or low power for a while during a landing, with the air flow turning the prop and cooling it, and abrupt power-up for a takeoff can "shock" it, that is when usually engines fail.
Dont get me wrong, I'll do a go-around in a second and engines are tough and this does not happen often, but the bigger the engine, the less you want to do that. Some flight schools even forbid touch & go's now.

By GVad The Pilot. Video Link.

Is it really bad to make touch & go's for the engine?
Do some flight schools really forbid touch & go's?
Are his concerns reasonable?

No. Touch and gos are fine. You can do touch and gos every day all day without hurting anything. I point to millions of hours flown on the GA training fleet and the average actual tbo of a flight school's trainers. The school I worked for used autogas and flew over 3000 on many of their engines. They were not unique. The idea that the engine sees some kind of benefit from "stabilizing" is questionable (would like to see data) and the idea that the engine is somehow "shocked" is nonsense.

Related

I'd question the uploader's belief that the engine even needs to "stabilize" after approach. I don't have any metallurgy-based reasons for believing this; just the fact that I've flown many airplanes that were doing touch-and-goes before I was even born and still didn't have so much as a hiccup when I was doing them myself. That said, most of the other responses have pointed to the fact that a full-stop landing does teach better piloting skills than t&gs do. But sometimes it's not the proper time to reinforce those skills; thus touch and goes.

As an automotive engine mechanic with 35 years of performance oriented experience and 29 years of that with ASE Master Certification and about a dozen other engine specific certifications.  Twenty or  so years ago I trained to be a piston engine aviation tech.
So I think I can say with some certainty that I know a thing or three about how engines work and what sort of things can have a detrimental effect on them.
"Thermal shock" is definitely bad for an internal combustion engine.  That said, touch & go's will not cause thermal shock to occur in a piston engine, here's why.
Thermal shock is what significantly rapid and drastically uneven temperature change in an engine is called.  This means if one or the other isn't occurring then there's no thermal shock occurring.
(To be accurate, it's more a degree of severity, as these conditions happen during normal operation and always will.)
The minimum operating temperature called for by the engine manufacturer is to avoid thermal shock.  It is important enough for the manufacturer to stress because it is the only reasonable condition the pilot can produce enough thermal shock to damage the engine.  When the engine is below the minimum, applying full power causes the pistons and rings to heat up and expand much more rapidly than the cylinders. This in turn reduces the clearance around the pistons and can dramatically increase the friction.  The increased friction compounds the problem by adding to the heat and expansion of the piston.  More expansion -> more friction -> more heat... This quickly becomes a deadly self reinforcing loop.  Because the pistons can't shed heat to the cylinders fast enough the cylinders don't expand and very quickly there's no clearance and the piston seizes up inside the cylinders.
Rapid temperature change in part of the engine without a matching change in the rest. This is the part of thermal expansion that breaks things.  The piston to cylinder heat transfer is very inefficient. But the transfer of heat, to the air from the engine, is even slower. So, once the engine is warmed up, it stays that way till it's parked in the hangar and you're headed out. That's just physics 101.
The alternative situation is not likely to happen and if it did, your last worry would be the thermal shock to your engine as the engine wouldn't be running long enough to get damaged, from heat shock that is.  What I'm talking about is full submersion of the engine in water. Given this scenario I am doubtful "thermal shock" would really be on your mind.  To be honest, I'm not sure if even the coldest water you could keep liquid is cold enough to chill the cylinders to the point of interference.
The belief that touch & go's cause too much "thermal shock" probably comes from mechanics understanding the cumulative effect of dissimilar thermal expansion caused by repeated full throttle application during the touch & go's, but being unwilling or unable to explain that it is really only an issue during the run-in period of time when the new rings are seating in freshly honed cylinders.
The only other way I can see touch & go's being an issue is if a freshly built engine is put together with too little clearance between the pistons and the cylinders.  In the extreme, repeatedly heat stressing the engine could scuff its way to a seized piston.  None the less, that wouldn't be thermal shock anyway.  That would be builder error and the probable source of stories that say "Touch & go's will blow your engine up!"

Is it really bad to make touch & go's for the engine?

Generally speaking, no. First off "shocking" an engine is generally referred to in the context of cooling it not heating it. For what its worth the consensus is that this is largely an academic debate anyway and may or may not actually contribute to engine wear. There is some logic that dictates that cold oil does not lubricate as well as hot oil but if the engine is running (even at idle) the oil is generally hot enough to lubricate properly. In this case the engine would have been warmed up, at first start the oil may be cold. According to continental the minimum oil temp for takeoff is 75F

Oil Temperature Limits

Minimum for Take-Off .... 75°F.

On your average spring/summer day that may very well be ambient air temp. But we can take a look at their cold weather procedure (below 32 F ambient air temp on the ground) for the really cold situation,

When the oil temperature has reached 100°F. and oil pressure does not exceed 80 psi at 1700 RPM, the engine has been warmed sufficiently
  to accept full rated power.

So as long as your gauges are reading within those limits on approach I see no reason a go around would be any problem.
Please note the above listed info is for one make and model of continental engine and you should always consult your aircraft's POH for the numbers relative to your aircraft's configuration.
On a bit of a related note, when doing a touch and go you should apply throttle smoothly and not just slam it forward.

Do some flight schools really forbid touch & go's?

Not that I have ever heard of but some airports do (usually as a noise abatement thing) so it may just be that the flight school in question does because the airport does. That being said the planes generally belong to the flight school, they can make what ever rules they so please.

Are his concerns reasonable?

Eh, depends who you ask. Reasonable, maybe, correct, unlikely. It should be noted that thermal shock is a real thing and it applies to both the cold to hot and hot to cold situations. The jury is still out as to what effect this, if any has on airplane engines (in both cases). As noted in the comments to the question there are a lot of trainers out there who have performed countless touch-go's and have had no issues.

To answer your questions 1) no, a touch and go will not harm the engine, provided it is operated within its established limits and not excessively pushed.  2) It all depends on the flight school in question; some do NOT want students attempting touch and gos, primarily in cases of a short runway the school operates from or just done intentionally to develop better habits in handling the airplane during airport operations. 3) I’m not sure what the guy means by “get the engine properly stabilized” so I can’t say anything about that.  Some pilots will like doing touch and gos while others will do stop and gos or taxi backs simply because they don’t like to be rushed with the added workload of a touch and go.

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Is there an audible warning on commercial aircraft if you try to land gear up?
In one of the comments on this question (under the accepted answer), someone remarks that

Aircraft can legally fly without a system to alert the crew when they are landing with gear up, etc.

Are these systems installed on commercial aircraft as a legal requirement?

Yes, you hear a loud scraping sound.

Sometimes the warning is the sound of the gear coming down...

All turbine-powered aircraft used in scheduled airline service under CFR Part 121 are required to have an approved TAWS installed;

§121.354   Terrain awareness and warning system.
(a) Airplanes manufactured after March 29, 2002. No person may operate
  a turbine- powered airplane unless that airplane is equipped with an
  approved terrain awareness and warning system that meets the
  requirements for Class A equipment in Technical Standard Order
  (TSO)-C151. The airplane must also include an approved terrain
  situational awareness display.
(b) Airplanes manufactured on or before March 29, 2002. No person may
  operate a turbine-powered airplane after March 29, 2005, unless that
  airplane is equipped with an approved terrain awareness and warning
  system that meets the requirements for Class A equipment in Technical
  Standard Order (TSO)-C151. The airplane must also include an approved
  terrain situational awareness display.
(c) Airplane Flight Manual. The Airplane Flight Manual shall contain
  appropriate procedures for—
(1) The use of the terrain awareness and warning system; and
(2) Proper flight crew reaction in response to the terrain awareness
  and warning system audio and visual warnings.

The TAWS system includes the functions of the older Ground Proximity Warning System (GPWS).
GPWS Mode 4, Flight Into Terrain with Less Than 500 Feet Terrain Clearance and Not in Landing Configuration, provides for alerts to the crew when entering a defined envelope below 500 feet (based on height and rate of descent) and the gear is not in landing configuration. There is also an alert envelope for Flaps not in landing Configuration.
The Mode 4 alert consists of an audible alert "TOO LOW, GEAR. TOO LOW, GEAR."

Is it possible to comment on the MEL requirements about an operative TAWS? It seems possible to fly with inoperative units which de facto make the TAWS inoperative itself. E.g: In this A320 MEL, page 34-2, IR1 may be inop, in this case "The terrain function of TAWS is inoperative". There are other occurrences. It would mean, if confirmed, that it's possible to fly some days with some TAWS functions inop, maybe the gear up condition.

@mins That MEL entry and a similar for FMGC 1 apply only to the 'Terrain' function which includes the FLTA function, PDA function, and Terrain Display function. They use A/C position and inertial vector compared to the digital terrain database to predict terrain conflict. The Mode 4 alert is a GPWS function. Look at 48-01 on page 32-21 for the limitations. It may be INOP if "alternate procedures are established and used and repairs are made within 2 flight days." A failure of Radar Alt 1 will also render GPWS failed - see 42-01 on page 34-18.

Thanks for having digged into the MEL and added your analysis.

What about over water?

@Mazura Unless you're flying a plane that can only land on water, and I'm not sure those are used by commercial airlines, you'll have to cross land eventually.

I'm just wondering if we should have heard GEAR in the movie Sully, or it wouldn't have because they were set in some landing phase?

@Mazura Is Sully worth watching? I've heard it's terribly inaccurate.

@Cloud its not any more inaccurate than any dramatization of a RW event. They perhaps spiced up the courtroom drama for cinematic suspense. Its not a documentary. It's good entertainment if you're into that sort of thing.

More basic than the TAWS requirement are the certification requirements for transport category aircraft, specifically 14 CFR 25.729(e)(2)

14 CFR 25.729 (e) Position indicator and warning device. If a retractable landing
  gear is used, there must be a landing gear position indicator easily
  visible to the pilot or to the appropriate crew members (as well as
  necessary devices to actuate the indicator) to indicate without
  ambiguity that the retractable units and their associated doors are
  secured in the extended (or retracted) position. The means must be
  designed as follows:
(1) If switches are used, they must be located and coupled to the
  landing gear mechanical systems in a manner that prevents an erroneous
  indication of “down and locked” if the landing gear is not in a fully
  extended position, or of “up and locked” if the landing gear is not in
  the fully retracted position. The switches may be located where they
  are operated by the actual landing gear locking latch or device.
(2) The flightcrew must be given an aural warning that functions
  continuously, or is periodically repeated, if a landing is attempted
  when the landing gear is not locked down.
(3) The warning must be given in sufficient time to allow the landing
  gear to be locked down or a go-around to be made.
(4) There must not be a manual shut-off means readily available to the
  flightcrew for the warning required by paragraph (e)(2) of this
  section such that it could be operated instinctively, inadvertently,
  or by habitual reflexive action.
(5) The system used to generate the aural warning must be designed to
  minimize false or inappropriate alerts.
(6) Failures of systems used to inhibit the landing gear aural
  warning, that would prevent the warning system from operating, must be
  improbable.
(7) A flightcrew alert must be provided whenever the landing gear
  position is not consistent with the landing gear selector lever
  position.

For the 767, these are the requirements to trigger a landing configuration warning.

(7) Landing Configuration Warning Module Function (Fig. 8)
  (a) The landing configuration warning module provides aural and visual
  warnings for improper airplane configuration during landing. The
  module receives a dual input of |12 volts dc and +5 volts dc from power supply modules A and B.
(b) The landing configuration warning consists of the master WARNING light, siren aural warning, CONFIG light, and level A EICAS message.
(c) The landing configuration warning logic is enabled when the module
  receives the landing gear not down and locked discrete signal from the
  proximity switch electronics unit.
(d) When this logic is enabled and  any of the following conditions occur, the landing configuration warning is provided. The outputs for each condition are as listed below:
1) The trailing edge flaps are set to 25 or 30 degrees: a) red master WARNING lights b) amber CONFIG light c) siren aural warning d) level A EICAS message
2) Both left and right thrust levers are set to idle and the radio altitude is below 800 feet: a) red master WARNING lights b) amber CONFIG light c) siren aural warning d) level A EICAS message
3) Either left or right thrust lever is set to idle, the radio
   altitude is below 800 feet, and the time delay as noted below has
   expired: a) red master WARNING lights b) amber CONFIG light c) siren
   aural warning d) level A EICAS message NOTE: A one time delay of 140
   seconds is triggered by the edge of the landing-gear-up transition
   pulse. This delay allows the airplane to reach an altitude of greater
   than 800 feet and prevents a warning if only one engine is throttled
   back at takeoff or go-around. If either 140 seconds have elapsed or
   the airplane has exceeded 800 feet altitude, the system reverts back
   to providing a warning from a single engine throttle back.
4) A radio  altimeter failure exists, either thrust lever is set to the idle position, and the airplane is in a clean wing configuration (flaps and slats are fully retracted): a) amber CONFIG light b) level A EICAS message
5) A radio altimeter failure exists, either thrust lever is
  set to the idle position, and either the flaps or slats are not fully
  retracted (NOT CLEAN WING): a) red master WARNING b) siren aural warning

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What was the motivation for revoking the licence to the pilots of Northwest flight 188?
This video describes Northwest flight 188, where two pilots overshot their destination by 150 miles, without contacting ATC for an hour. They cited 'cockpit distractions' as the reason and subsequently, both had their licenses permanently revoked.
What exactly was the license removal be for? Overshooting the runway? Not contacting ATC for an hour? And what are the quantitative rules on this, i.e. how long would you have to not contact ATC for or how many miles off course would you have to go to get your license revoked liked these two did (in a commercial setting)?

Overshooting the intended destination isn't exactly a runway overshoot, whether you're using the US or (apparently) UK meaning of the term "overshoot".

According to this CNN article the FAA revoked their licences with a letter containing the following reasons (emphasis mine):

The letter said the pilots were "extremely reckless."
"Not only did you not comply with ... [air traffic controller] instructions, you did not even monitor the aircraft's air-ground radios," the letter said. "You were disengaged and impervious to the serious threat to your own safety, as well as the safety of people for whom you are responsible. This is a total dereliction and disregard for your duties."
[...]
The FAA said the revocations cite several violations of regulations, including failure to comply with air traffic control and clearances and operating carelessly and recklessly.

As Adam pointed out in the comments, this would violate FAR 91.13:

§ 91.13 Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.
(b) Aircraft operations other than for the purpose of air navigation. No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.

I take it there is no regulation set in stone and the FAA has leeway to decide what extremely reckless means on a case-by-case basis?

@AEhere yes, I would assume so, too. There won't be any quantitative rules for this. The authorities (in this case FAA) will evaluate the severity of the incidence and then make a decision, which can however be appealed by the pilots.

@AEhere That was my question. I wonder if these pilots did appeal and what the full story really is...

@Cloud have you read the wikipedia article and the references? what is it missing there that you are wondering "what the full story really is"?

@Federico Yes.. why was there was only 30 minutes' worth of information on the voice recorder? What exactly were they doing on their laptops? Why did none of the cabin crew say anything sooner? (Or any passengers for that matter) Do the pilots in question still fly in any capacity today? If not, what is their profession(s)? Were police forces present when the aircraft landed?

Their distraction cover story was quite unbeleivable.  Most professional pilots will tell you the likely truth was they both fell asleep. It's the explanation that makes the most sense.  The crew of a CRJ200 once both dozed off following a departure from an airport in Hawaii, for about 15 min.  One was just exhausted from circumstances that resulted in poor sleep the night before, and the other had undiagnosed sleep apnea and depending on coffee.  The 188 crew likely decided that taking the heat for inattention was better than admitting they fell asleep; didn't work out for them.

@Cloud It's possible for the capt to reset the CVR, which erases it, but which is a very very bad thing to do.  Which would explain only 30 min recorded and would be another large strike against them.  The sanction was pretty severe, especially for the FO, and I'm convinced it was because the authorities had surmised what really happened and were pretty unhappy with both of them sticking to an implausible story line.  If they had passed out and admitted so, they would have gone for medical assessments but probably would have had a better outcome.  Someone gave them very bad advice I think,

@JohnK That's what I've always thought. But I think screwing around on their computers is actually worse than falling asleep.

@JohnK Thanks for the clarification, that really makes a lot more sense to me now :)

@Cloud It's interesting. Aviation is one of those fields where, because decisions are life and death, trying to BS your way out of trouble rarely works.  Screw ups made in good faith, even things like dozing off, (which people in cars do all the time) usually get the screwer uper cut a bit of slack insofar as the remedial actions will be rehabilitative as opposed to banishment from the trade.  It's the liars that really get hammered.

If this had been a private pilot in a C550, he may have merely gotten a slap on the wrist, but probably would have had some sort of adverse action taken. The big issue here is flying passengers for hire in conjunction with ignoring (sleeping through) ATC clearances. THAT is why the action was so severe.


text:
Where does the transponder read altitude, or does ATC get it from radar?
When flying instrument approaches in a rented plane, Approach called out an altitude discrepancy between the assigned altitude which is being flown using the altimeter and the altitude being reported by the Mode 3/C transponder.  Back at the hangar, the question is: does the aircraft have or need an encoding altimeter interfaced to the transponder to report altitude, is it built into some transponders; or was the Approach controller using altitude as reported by the radar if it has height finding capabilities?

Possible duplicate of How are airspace violations detected?

does the aircraft have or need an encoding altimeter interfaced to the
  transponder to report altitude, is it built into some transponders

In order to squawk mode C, you need an encoding altimeter connected to your transponder and the transponder needs to be set to transmit mode C. Does that transponder have a build-in encoding altimeter? That requires a check through the logs and/ or manuals. In my aircraft they are separate, in yours I have no idea.

or was the Approach controller using altitude as reported by the radar
  if it has height finding capabilities?

Maybe. It depends upon the specifics of the airport. If your transponder's altimeter was calibrated incorrectly or otherwise bad (extremely difficult for you as the pilot to verify in a rental aircraft during preflight) then they may have been trusting your transponder for your altitude data, which was incorrect. If they were using radar with vertical capabilities (precision approach radar is, depending upon your viewpoint of part 91 vs part 121, either relatively rare or everywhere you might need it where I live) they may have been comparing that to your transponder's altitude reported.
All of this depends upon if you checked your altimeter using the current local setting on the runway threshold prior to takeoff. Have I always done that? Yes. Does everyone? No. If your panel altimeter checked out, you used the proper setting during the approach, and your transponder is telling them you are at the wrong altitude the transponder's altimeter appears to be the problem.

If the ATIS is old and a front is passing through, it could be enough for a 50 or 100' difference between what the field is reporting as the altimeter setting and what the automated system ATC uses is reporting.

Very true, I keep forgetting that I am spoiled with one minute ASOS updates at my home field. However, if that is the case then everyone's altitude should be off by the same amount and typically ATC will announce a new altimeter setting on the approach frequency if that happens.

@RudyB: ...assuming, of course, that there aren't any localised spikes or dips in the atmospheric pressure around the airport.

@Sean any significant spike or dip in atmospheric pressure will be accompanied with severe weather nobody is going to miss—less so fly into, because it will look (and be) dangerous.

I'm no expert, but from what I gather the transponder has a direct connection to the altimeter pre-Kollsman window. Not sure how that's possible but it's something along those lines.
Essentially the transponder reports your flight level to ATC no matter what— it always reports your altitude assuming an altimeter setting of 29.92. Then the radar system on the ground corrects that given the current altimeter setting in your area, which can be manually entered by the controller but is usually updated automatically. The controller asks you what you're seeing in the cockpit, and hopes that 1) you've entered the altimeter setting properly and 2) what you see matches what the scope shows (bearing in mind it only displays to the nearest hundred feet).
The two numbers might not match perfectly because of issues in the transponder's calibration or other such problems. If the mismatch is 300 feet or more, you will be asked to discontinue altitude squawk (squawk ON or NORMAL instead of ALT) and the controller will manually input a "pilot-reported altitude" on your data tag and ask you to report prior to changing your altitude. They're assuming what you see in the cockpit is correct and what the transponder reports isn't, so please make sure you have the correct altimeter setting!
Unless you were talking to a super-fancy military approach control, they were not using the actual radar system to determine your height above the radar site. Civilian radar systems only provide azimuth and range, not elevation; they rely on aircraft-reported SSR for altitude information.

Mode A/C Transponders were originally implemented because the best you could get from skin reflection radar was a slant range altitude that wasn't very accurate. The altitude that a mode A/C transponder transmits with when swept by a Secondary Surveillance Radar or that a Mode S transponder autonomously squits (transmits every 1/4 sec) is pressure altitude.
Pressure altitude is the altitude indicated by a barometric altimeter with the Kollsman window or barometretric offsett set to 29.92 inches HG.
In older aircraft, there could be an encoder that provides the signal to the transponder over a parallel bus using machine code. In more modern aircraft it would come from an air data computer over a serial bus like ARINC 429 OR 629.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why does AH-64 Apache have its radar over its rotors?
The targeting radar is above the rotor assembly !

But why ?

See Do helicopters carry radar equipment? Is so, where is it placed and what type is used?, possibly a duplicate.

Because it's a good view point there.

Because this allows it to "peek over" an obstacle while hiding behind it.

Mostly so the hovering helicopter can stay below the sight line, and missile trajectory, of the enemy...example


text:
Is aviation slowly dying as of 2019
This debate first started a decade ago but I want to modernize it.
The reasons people wanted to be pilots. (I cant find a single reason why someone would want to become an ATC)

They watched Top Gun etc. and decided to be pilots.
Their grandparents were WW2 Veterans which fascinated them with war stories.
They simply loved seeing planes that flew above their homes.
They liked the WW2 pilot stories on the school.

Problems these days.

Aviation movies are getting rarer and rarer and the millenials love watching nothing other than Ninja's Fortnite streams.
There isnt anyone to fascinate the kids with their war stories.
Since people are doing nothing but sitting on PC's and playing Fortnite with noise cancelling headphones they dont even see planes.
Since social media stories are better than the history lessons they get fascinated only by the success stories of Elon Musk etc.
All of this cumulated with the ever increasing pilot school fees and lack of interest of aviation where people act like animal herds where they will do their best to stay in a group like a dog that will never leave their owner kills the indivuality where the group leader is the role model for everyone else.

The final hypothetis is: Since nobody will want to become pilots this industry will be taken by the 1 pilot Artifical Intelligence planes (Altough the transocean hyperloop will balance) and the general aviation (Especailly Private Aviation with 100 percent of self flying pilots will die) will suffer trendmeous failures plus there are "rumours" of ATC being taken over by AI and humans only interfering in emergencies
I know this question seems like an some other broad and opinion based question but I think the next paragraphs can solve this problem.
Long story short. What I really want to find is an answer that includes some charts and infographics that will show the rate of people getting pilot certificates over the years.

This question is very broad and opinion based, I can't see it having good answers.

The original US astronauts insisted on a window being installed on the first capsules. That was so they could pretend, to themselves, they were pilots not passengers.

I can't see a single reason why someone would want to be an accountant but the accounting sector isn't going anywhere.

@Ben so I guesss some "crazy" people that loves stressing themselves over "boring" jobs that are nothing more than sitting all day solving questions exist.

Your question made me laugh. I get why you're saying what you're saying... But you didn't have to generalize and throw everyone (I'm assuming this is directed at the latest generation) in the same lazy bucket because all you see is video games and headphones. You also make some claims about interest waning over the whole world (aviation is global). I'd like to see info graphics about this, too. From you. - 1

@Pheric even if we say birth dates are staying stable through the USA (Altough states are different in rate) the number of people are slowly decreasing. Altough this generation (15 to 20 year olds) are doing some fine stuff the next gen (0 to 15 year olds) that have enough intellect to play Fortnite (I am joking plus it became a disease so not so bad). The mass automation will probably crash so many industries which will make the people spend a little bit more money on basic needs (Unless people  have gold deposit plans like me) and from little bit interest people to dreamers will get hurt.

@JonathanIrons nobody knows any of that for sure, because it's not that bad yet. The best we can do is trend what it is today and pretend that the trend will hold true, which it probably won't. And don't forget that trends like fortnite are how life is. When you were a child, you probably played games and such too, but you didn't stop dreaming and you grew up (probably). Even if becoming a pilot isn't as popular as it once was, it might only take a large event to spark that interest in people again.

I find your question extremely biased and offensive. I'm the generation you're talking about, and I don't waste my time on useless things like playing Fortnite all day or wandering around the internet. Sure, some people does that, but obviously not all, and not just our generation either. It is simply because the new generation have more continued, stable and reliable access to the internet, that's all. In fact, older generations also do boring or useless things sometimes, it's just a part of being human.

And I don't see how all this biased statements of yours have anything to do with what you're trying to ask, either.

Additionally, there's simply no way on earth Artificial Intelligence can take over the job of pilots or ATC. It'll be fatal at 100%. I'm a programmer, so I know what AI can do and what it can't. Another thing you're incorrect about is that older generations become pilots not because of Top Gun, world war II ace pilot stories (probably a bit, but certainly a very minor contributing factor), or some grandparent's stories, but mostly because of their passion for the skies and love of the grand, fast aircraft streaming through the clouds. And this basically won't change much between generations.

I believe the information that you are looking for can be found in this AOPA Report.  Basically aviation is on a rebound.  The report compares available data from 2015 to 2017 and the amount of pilot certificates being issued in the Private, Commercial, CFI, and Instrument ratings all increased.
A side note about your comments on there being less aviation movies and references in Pop Culture.  There are actually a ton of very good YouTube channels out there on Aviation and have inspired many (myself included) to become pilots.

thanks for sending me the tottally objective AOPA report and good luck in your future endavaours plus it makes me happy to see people that does something other than playinf Fortnite.

Not according to Boeing.  They see a need for over 40,000+ new aircraft over the next 20 years.
Ranting aside, it might be a good idea to think about why someone would want to be a
PROFESSIONAL pilot.  Maybe a little more than movies and grandpa's stories.  Maybe a little more like a commitment to a career.
If you are at a computer and proficient enough to ask the question, references and resources are only a click away on another tab.
For the younger, R/C flying offers a huge head start in learning the fundamentals of flight.
There are also many flying schools geared towards training future airline pilots.
Yes, automation is making inroads in control of aircraft, and it will be a challenge for the engineers and pilots to decide how much is actually needed.


text:
Why isn't the Presidential 747 "Air Force One Heavy"?
Aircraft with a maximum takeoff weight of at least 300,000 pounds add the word "Heavy" to their callsign.  (Example: Lufthansa 415 Heavy in this video.) The current Presidential 747's have a maximum takeoff weight of 833,000 pounds.  Yet, it flies (when the President is on board) with the callsign "Air Force One", not "Air Force One Heavy."
Why not?

100% purely anecdotal and probably not true, but: I had an instructor (retired controller) tell me he knew the guy who caused the rule change. This guy was working AF1, kept calling him "heavy" as required by the book, the pilot (an Air Force major) got offended and by the end of the day there was a new rule saying AF1 should not be called "heavy." It would be interesting to pore over old versions of the 7110.65 and see when the rule was added.

FAA JO 7110.65 Section 4 Radio and Interphone Communications specifically states that the "heavy" designator should not be used:

e. When in radio communications with “Air Force One” or “Air Force Two,” do not add the heavy designator to the call sign. State only the call sign “Air Force One/Two” regardless of the type aircraft.

I speculate that the reason for only using the callsign, not heavy, is additional security against identifying the aircraft that POTUS is on. If it's never called heavy, the absence of the designation tells radio interceptors nothing.

@Nij I was under the impression the call sign of an aircraft is "Air Force One" if and only if the POTUS is on board.

@Nij How should that work? Please elaborate. Even if, for some reason, the president could decide to fly with a Gulfstream exec jet (he can't, Secret Service won't allow), and the empty AF 28000 is starting at the same time from the same airport, the call sign AF 28000 gives away that AF 1 is a different plane right now...

Yes, but if you called AF1H instead of just AF1, that immediately says POTUS is on the bigger of two (or one of the bigger among many) aircraft. By only ever saying AF1, there is never a hint as to whether it's an aircraft with Heavy designation or not. However, Alexander torpedoes the idea with the obvious deduction-by-elimination point.

@Angew: Not "an aircraft", only some aircraft: the call sign of any and all US Air Force aircraft that the president is currently on, is "Air Force One", only for the time the president is on it. (See the final climax of the eponymous Harrison Ford movie for a heavily dramatized but surprisingly accurate example – the only realistic second of the entire movie.) If it is a US Marines aircraft, the callsign is "Marine One" instead. For a US Navy aircraft, it is "Navy One". For a commercial aircraft, it is "Executive One".

A good example - when it was made very obvious - is how the plane flying Pres. Richard Nixon changed it's call-sign in mid-flight from "Air Force One" to SAM27000 (it's "real"/normal call-sign) at noon, when Nixon's letter of resignation took effect and Ford became President.  Also the same system for "Marine One" - the helicopter... and if the President was on a navy-ship (or I assume a navy-plane), it would be "Navy One".

@Alexander The Secret Service can't give orders to the President, they serve under him, not the other way around. If President Trump wanted to fly on his own private jet no one has the authority to stop him.

@Nij I seriously doubt the lack of heavy designation has anything to do with security. If that were the case why give the president his own call sign at all? If subterfuge was necessary they would simply leave its designator as it is when he's not on it and not paint it with special livery. The whole idea of the AF1 designator is to indicate its protected status.

it is not as if other aircraft are going to be allowed near it What does this even mean.

@digitgopher It means what it sounds like - no other aircraft will be allowed to follow closely enough to Air Force One for its wake turbulence to be a concern (at least not in the U.S., anyway.)

@reirab I'm unaware of any special separation rules for Air Force One. What ensures no other aircraft will be close enough for wake turbulence to be a factor?

@digitgopher do you think when AF1 flies, they let other planes get close enough to be in its wake? As for what ensures no other aircraft gets close, I'm sure the Air Force fighter jets that fly with it provide a good enough deterrent :P  Edit: Here's an article mentioning the FAA is investigating a plane that came within 3 nautical miles of AF1 this month.

@Alexander the President is the Secret Service's boss. He tells THEM what to do, not the other way around. They will strongly recommend that he doesn't fly any jet besides AF1, but he has the final word

@digitgopher I'm not sure about the specific rules, but most of the times I've seen where Air Force One was moving on the field, all other movement was stopped, even at major international airports.

@BruceWayne - can you check that link, please. At the moment, at least, the domain isn't found.

@FreeMan ah, odd... Here's a link to Bloomberg, hopefully it stays up.

My understanding was that "heavy" was used to describe aircraft full of passengers or cargo.

@Devil07 your understanding is incorrect, it is based on the certified maximum takeoff weight and nothing else.

@randomhead. I have revised my understanding of the term "Heavy" I know understand it to be: Heavy− Aircraft capable of takeoff weights of 300,000 pounds or more whether or not they are operating at this weight during a particular phase of flight.  LOL

@BruceWayne movement on an airport is indeed very limited when AF1 arrives and is on the ground, but there are no special separation rules for AF1 while airborne. digitgopher is entirely correct. You can watch ADS-B Exchange some time when the POTUS is flying into a large busy airport and see. (The point being, the increased wake turbulence separation required behind a heavy may well be relevant.)

Similar ping @reirab. Nothing says that AF1 gets special separation beyond the standard 3 or 5 NM. Of course, if that separation is lost many people will be very interested, as BurceWayne's link alludes to.

@randomhead I was assuming that taking off or landing behind it within the delay times that would normally apply to a heavy arriving or departing in front would be difficult to do when you can't taxi while it's moving anyway. Do they actually send arrivals or departures in/out within a few minutes of AF1?

@reirab operations in the Terminal environment are not limited to taking off and landing; aircraft may be climbing, descending, or in level flight while still within Terminal-facility-owned airspace (in which the "heavy" would normally be spoken by ATC). These aircraft are not restricted from flying during the time when AF1 is not on the ground. And as I said, you can see for yourself next time POTUS is arriving at or departing from a busy airport—there may be stragglers operating as the TFR is activated.

@randomhead Yes, I'm aware that they don't clear out the whole terminal area before it enters, but the vicinity of the runway environment is where wake turbulence concerns are most important. Even farther away from that, though, I'd have assumed that no one would be following closely behind AF1, either inbound or outbound. Its wake shouldn't be especially relevant to aircraft arriving ahead of it or those departing while it's on approach under most circumstances. I will try to take a look at ADS-B Exchange sometime when POTUS is going in or out, though. Sounds interesting to watch.

The purpose of the "heavy" designator is create situational awareness because of its wake turbulence. There are also different separation requirements when following a heavy aircraft. Since all air traffic around Air Force 1 is likely to be heavily controlled, there's no need to call out that it's a heavy.

Also worth noting that there's only one aircraft of it's kind to worry about at a time. It's like tacking qualifiers onto a space shuttle on re-entry.

-1. Air traffic around busy airports is always "heavily controlled" but the "heavy"/"super" suffix is still used. What source do you have for the claim that AF1 receives any additional separation?

@randomhead You should not be asking for a source when the answer is common knowledge.  https://aviation.stackexchange.com/questions/1689/how-does-atc-protect-air-force-one

@Anon nothing in those answers, and nothing in the 7110.65, gives any indication that it is against the rules for an aircraft to be operating closer than 4NM of AF1 (but still 3NM or greater), wake turbulence considerations aside. Once you have a Heavy, Large or Small operating directly behind AF1 and 1000ft (or fewer) below, wake turbulence must be considered and more separation is required. Hence the purported benefit of the "super"/"heavy" designator—situational awareness for the pilot following—would still be applicable.

@randomhead Read the link again.

@Anon obviously you see something there that I don't. Please quote exactly what part of the link is "common knowledge" and the source for a claim that ATC provides additional separation to AF1 beyond standard IFR separation.


text:
Does ATC direct flights to fly eastbound at odd levels and westbound at even ones?
Do commercial airlines routinely travel at altitudes specified by the ATC based on the direction they are heading? Example: eastbound flights travel at odd levels and westbound flights travel at even ones?

I remember there was another question here addressing this, I just can't pick it out.

Please consider clarifying your question if you do not feel the provided answers include the information you were looking for.

In addition to ymb1's excellent answer, here are a few thoughts from the controller perspective.
Various rules and regulations for cruising level allocations exist. For flightplanning purposes, the semicircular rules are very notable. As pointed out by ymb1, the exact rules vary from place to place. In some regions, flights flying on a westbound track shall plan to fly at even levels while flights flying eastbound shall plan to fly at odd levels. Note that this is in relation to the magnetic track of the aircraft, except in areas near the poles. In some countries it is the other way around, in others, the rule is north/south instead of east/west.

Example of a general east-odd/west-even rule (excerpt from AIP Denmark)
You can also have specific ATS routes, such as airways, that require you to flightplan certain levels that deviate from the general rule.

Example of ATS route which enforces even levels for eastbound flights (excerpt from AIP Germany)
It is important to note that rules for level allocations are mainly used for planning purposes. When filing a flightplan, the planned levels must obey any such rules - and you should always stick to your filed flightplan when in uncontrolled airspace.
However, when being provided with air traffic control service, the controller may deviate from the general rules if so desired (unless the local operating procedures do not allow it). If I have an upcoming conflict that can be solved by climbing a westbound flight to FL370, then I will be more than happy to do so - especially because establishing vertical separation is often the easiest way of solving a conflict. As long as the flight is within my sector, then I make the rules, so to say.

Example of ATC radar screen with eastbound traffic (SAS528) flying at an even level (FL340) for separation
When transferring a flight to the next sector (or another unit), the controller is responsible for making sure the flight is at an appropriate level in accordance with the local letters of agreement. Principally, this means that we have to go back to the published rules (east odd, west even or specific airway rules). In practise, though, if it is desired to transfer a flight on a non-standard level, all it takes is a phone call to the next sector to check if they can accept it. If the next sector has no conflicting traffic, then there is nothing wrong with keeping the flight at a non-standard level.
So to sum it up, when planning a flight, you have to obey the published level allocation rules, which vary from place to place. A large part of the world uses the east-odd, west-even rule. But once under ATC control, there is no need to worry if you are assigned a non-standard cruising level - if that happens, it is because it is allowed and has been coordinated.


text:
Where is the 36 month ATPL theory exam validity before CPL/IR test listed and described?
The provider of my EASA Integrated Training Course states that my ATPL theory exams are only valid for 36 months before a CPL or IR skills test.
Where is this regulation listed and described?
Additionally, is this from the date the ATPL theory series is completed, or when the earliest ATPL exam is completed? Finally, do both the CPL and IR skills tests both have to be completed within 36 months, or, just the CPL?

I don't know much about EASA regulations, but this seems to be a reference to Part FCL.025(c)(1):

(1) The successful completion of the theoretical knowledge
  examinations will be valid:
  [...]
  (ii) for the issue of a commercial
  pilot licence, instrument rating (IR) or en route instrument rating
  (EIR), for a period of 36 months;
  (iii) the periods in (i) and (ii)
  shall be counted from the day when the pilot successfully completes
  the theoretical knowledge examination, in accordance with (b)(2).

Having said that, (c)(2) gives a much longer validity period for the ATPL exams:

(2) The completion of the airline transport pilot licence (ATPL)
  theoretical knowledge examinations will remain valid for the issue of
  an ATPL for a period of 7 years from the last validity date of:
  (i) an
  IR entered in the licence;
  or (ii) in the case of helicopters, a
  helicopter’s type rating entered in that licence.

My understanding of that is:

Your IR theory exam is valid for 36 months from the date of the exam
Your ATPL exams are valid for 7 years from the date you receive your IR (although the wording is ambiguous, in my opinion)

It's possible that your provider is combining those two points somehow. The easy thing to do here is simply ask them to explain their statement in more detail and include a reference to the regulations.


text:
What does the phrase "electrically controlled and pneumatically operated" mean?
While studying the air-conditioning of the A320 from the FCOM I came across the information that the pack flow valves are "electrically controlled and pneumatically operated". I can not understand what it means.

Human bodies are "brain controlled... muscle operated".  You think of something to do, the brain sends the signal and the muscles respond to accomplish the action.  The electricity (solenoid valve) is the brains of the operation while the pneumatic servo air is the muscle to move the valve

It means that an electrical switching signal is used to drive the pneumatic or air valves in the air conditioning system.
Think about it like this: We want to use our garden hose to push open a cat flap but we want electricity to control the pressure in the hose. We could apply an electrical signal to a motor which opens the tap and lets water come out. This water pressure could then be used to control how wide the cat flap opens. The only difference in your airbus situation is that it isn't water (which would be hydraulics), it's air that comes out of the tap (Pneumatic means air). So this system would be called an electrically controlled, hydraulically operated system. Substitute the water in the hose for compressed air and you have your answer.
The way electrically operated valves work is generally based on the principles of electromagnetic force by utilising  some sort of coil. This setup turns a piece of wire into an electromagnet, which is attached to or interacts with the movable part of the valve. This then ports air pressure to one side or the other, to balance open the valve to a set amount in proportion to the original electrical signal.
So we use electricity >>> this changes the balance of air >>> the air opens or closes the valve.
The valve can be fully open, fully closed or anywhere in between.

Re, "We want to use our garden hose to push open a cat flap..." Strong contender for the most thought provoking analogy of the day.

Well, I would prefer my cat to water the flower beds:)

@SolomonSlow Glad you liked the cat flap analogy! I teach avionics for a living and I always used to hate the textbook answer. My instructors really sucked when I went through so I try to make classes as enjoyable as possible, even though the material can be dry sometimes

So garden hoses are your answer to dry material; yup, that checks out.

@PeterCordes it's an analogy that everyone understands so that is what I went with. If you think there are any better ones out there let me know

I like it and am just playing along with your joke :)

They're called "magnet valves".  They're basically a valve that's operated by a solenoid.
Also seen on locomotive electrical contactors. The solenoid admits air, which moves an air piston which physically actuates the device. Doing that pure electrical would require gigantic solenoids, heavier wiring, heavier generator.
One thing to note is that unless your RAT generates compressed air, you lose your engines, you lose your air, and the electrical signal will no longer actuate it.  I suppose on an A/C pack it hardly matters.

Railway trains (electric multiple units mainly) used to have 'straight air', or Westinghouse brakes. The brakes were applied by air pressure, using a 'train pipe' charged with pressurised air. If the driver lowered the pressure in the train pipe, a valve on each coach opened and compressed air from reservoir tanks operated pistons to force friction shoes onto the wheel treads. The reduction of train pipe pressure took a certain time to propagate along the train. and electro-pneumatic air brakes were developed, where solenoid valves on each car operated instantly and all at once.

One reason EP brakes were attractive is that they reduced stopping distance, so trains could run harder, and brake later, between stations, and thus more trains per day could be run on existing infrastructure, so more tickets could be sold.


text:
What are the names of the antennas which I have marked in this picture of a Boeing 737?

I have taken the picture from PMDG 737NGX Microsoft flight simulator X. I am really curious to know what this antennas are. These antennas are behind the nose gear.

ATC, Altimeter Transmitters and Receivers, and DME-1


text:
Is there a general approach for designing a Trimmable Horizontal Stabilizer?
What is the general design flow when designing a Trimmable Horizontal Stabilizer (THS) and the attached elevator?
I assume you would dimension the max. positive/negative deflections of the THS to meet longitudinal trim requirements over all cg ranges, airspeeds, flap configs and then add the elevators on top of that to fulfill the manoeuverability requirements (pitch rate). But I guess there is more to it.
In other words:
How do you derive the maximum deflections of THS and elevator each?
(compared to a non-moving stabilizer design)
I'm not asking for specific formulas, but rather for the general approach. If you can recommend some detailed references about it, I would be really thankful.

You always look at both in combination.
The first step is to use tail volumes that have worked before. This is enough for preliminary design.
When the design advances further, you have load cases to cover which combine trim and manoeuvring demands and you use trim settings and elevator deflections in combination. The useable deflection range changes with trim settings, because when the tailplane needs to produce a sizeable downforce to trim deflected fowler flaps on the wing, it cannot tolerate the same positive elevator deflection as in straight flight with lightly loaded tailplane.
Also, speed, load factor and loading determine the downwash angle on the tail. The useable stabilizer range varies with the downwash angle, so each load case needs to be looked at by itself.
Next, you pick the tailplane size and deflection range which covers all load cases and verify the result in the wind tunnel and flight test.

Trimmable Horizontal Stabilizors vary from plane to plane.  For instances, the Cessna Cardinal has a small tab on the back of the stab that is changed by the pilot using a trim wheel in the cockpit. At high speeds, like 125 knots/145 mph, the Cardinal requires quite a but of push or pull the to change pitch - if you want to climb, you can haul back on the yoke, then dial in some trim to hold the pitch angle.
Compared to many Piper Stabilators, it does not expand the full width of the stab.
The deflection is designed to be enough so that don't have to hold the stick back while coming in for a landing. Coming down final, you dial in enough trim to fly a steady descent, and then still have stick control left to deal with minor up/down changes as needed from wind burbles & stuff, and then be able to pull back to complete the landing flare.
(Top picture is Piper, bottom is Cessna).

Please include image sources. Also, Cessna N3? That must be an ooooold plane!!

Appreciated, but I was more reffering to an engineering perspective on THS like they are used in large transport aircraft (Airbus, Boeing). Thanks, anyway!

First is understanding the horizontal stabilizer's function relative to its partner, the wing.
Jockey and horse really, perhaps director and symphony.  For passenger rated aircraft (and big cargo transports who really don't want to spill the goods), a general approach to design parameters may begin with the following criteria:

To control wing AOA and prevent the wing from reaching a stall AOA uncommanded.
This means the Hstab must be adequately sized enough to act as a "weathervane",
keeping wing AOA (relative wind) constant.
To keep net center of lift from drifting too far forward as angle of attack increases.
  As the wing pitches up, it's Clift moves forward, but as Hstab begins to contribute tail
   up/nose down torque, properly balanced, the effects cancel.
In the event of a full blown stall/sink, to pitch nose down faster than vertical descent
  increases AOA.  Failure to do so puts plane into "deep stall".

Designers have a choice of the airfoil approach, the larger flat plate approach, or a combination of the two.  A low aspect flat plate might be a safe choice for 3, as it acts in a manner similar to a parachute to push the nose down even if it is fully stalled.  Airfoils will work for 1 and 2, but must stall at a higher AOA than the wing.
Once the right area is established, determination of maximum deflections may be as follows: no one deflection should be so great as to not be overcome by two others.  This is why 3 pitch controllers may be better: Hstab pitch trim (very slow), elevator (weaker than Hstab in normal flight, higher rates available for emergencies), and a fine trim tab (for minor pitch adjustments such as a few knots of airspeed). The pilot(s) control the elevator.
If Hstab is designed properly and thrust line is correct, this should make for a very safe and stable aircraft.  Although obviously influenced by recent events, a review of basic designs can help engineers stay anchored near the highest of safety standards required for passenger carriers.


text:
What is the lightest jetliner out there?
What is the lightest commercial jetliner out there? I was thinking of something like a Embraer E170.

Does "commercial jetliner" mean a turbojet or turbofan aircraft in current use for scheduled passenger flights?

@Pondlife: Is there something else it would mean?

@Sean I don't know, hence the question :-) Especially if you don't know much about aviation, a "jet" could be almost anything. I once saw an article in Indian English that referred to a pilot "hovering" over Delhi in "a jet". She was actually flying a C150.

The smallest jet used in scheduled airline service that I am aware of is the Beechjet, but the service was stopped sometime last year, I believe.

Remember that even very small aircraft can be, and are, used for commercial flights. One example would be the Britten-Norman BN-2 Islander, used on the shortest commercial flight in the world between the Scottish Islands of Westray and Papa Westray, a distance of 2.7 km.

Do you count turboprop engines as jets? In that case, the lightest might be the Britten-Norman BN-2T, with an operating empty weight of 1667kg and a maximum take-off-weight of 3175 kg.

It depends on what you mean by ‘jetliner’.  By that term I would have to define it as a turbojet powered aircraft which holds a transport category type certificate.  A Dornier 328Jet with an OEW of 9420kg would be a good choice.  If you consider jets used for commuter operations, a Dassault Falcon 10 at 4400 kg, or an Aerospatsiale Corvette at 3510 kg would be a good choice.


text:
Is it ever allowed to list your destination airport as the IFR alternate too?
Is it legal (in certain conditions) to have your primary airport of intended landing, also listed as the alternate?

No. But you can use the airport you take off from as your alternate, if fuel allows.

Legal in what jurisdiction?

No offense, but you are asking about the legality of something that makes no sense whatsoever if you understand the purpose of an alternate.  It's like asking if your front tire can be considered as a spare for the back tire.  Sure, it can be, but if you get a flat the car is still stuck without a spare...

Why was this closed as a duplicate of https://aviation.stackexchange.com/questions/389/is-an-alternate-airport-always-required-when-flying-internationally? They look like completely different questions to me.

@JScarry It is legal for Part 91 flights to take off from airports below minima for landing and thus can't use as an alternate.

You would never list your destination as an alternate (that wouldn't logically make sense), but there are situations where having an alternate is not required:

At least one destination alternate aerodrome must be designated and specified in the both operational and ATS flight plans if a flight under IFR is going to be made unless one of the following applies:

after taking all relevant factors into account, it is reasonably certain that VMC will prevail for the approach and landing and there is more than one independently useable runway available which can be expected to be useable at the ETA and at least one of those runways has an instrument approach procedure

the aerodrome is isolated, in which case a destination alternate is not required and instead additional fuel must be carried. a Point of No Return (PNR) must be determined and this must not be passed unless an assessment of the prevailing weather, traffic and other operational conditions indicates that a safe landing can be achieved at the ETA.

Source: https://www.skybrary.aero/index.php/Alternate_Aerodrome (ICAO Annex 6 Chapter 4)

See also: Is an alternate airport always required when flying internationally?

The definition of "alternate airport" in 14 CFR § 1.1 is:

Alternate airport means an airport at which an aircraft may land if a landing at the intended airport becomes inadvisable.

If my intended airport is Sparta, then clearly Sparta itself is not "an airport at which an aircraft may land if a landing at [Sparta] becomes inadvisable." So the intended airport cannot be an alternate airport.
Now, there doesn't seem to be any regulation which explicitly says that you're not permitted to list your destination as your alternate. But 14 CFR § 91.169 says that a flight plan is required to include "an alternate airport," and a common-sense reading of this regulation says that the airport you list must actually be an alternate airport. If you say that your destination is Sparta and your alternate is also Sparta, then you have not satisfied the requirement to specify an alternate airport.

If your intended airport is Sparta, you can always list Hell as your alternate. Not that they had any concept of such, but this had to be said.

Well, for what it's worth, I'm pretty sure the closest airport to Hell is Richmond Field (8D4), which I fly out of regularly...


text:
How can I identify airliner types that don't have ACARS?
Is there a way to identify what commercial airliners are still flying without ACARS today? Most modern commercial airliners are equipped, but I know some 737s still fly without ACARS, for example.

Related: How do I track and visualize aircraft from home?

This question could use some improvement-- there's a whole lot more to the world of aviation than just business aviation plus commercial airliners.  It's far from accurate to say "Most modern aircraft are equipped" (with ACARS).  Substitute "what models of commercial airliners" for "what aircraft models", or something like that.  In other words if we were doing set theory, and we took the set of all aircraft models, and we subtracted away those related to business aviation, we'd still have many aircraft left that look nothing like what you are visualizing in your question re ACARS.

Modified the question

ACARS is a operator specific (optional) system. It depends on the operators requirements if an aircraft is equipped with ACARS or not. You can't tie it to an aircraft model or variant. As a rule of thumb: The older the aircraft, the less likely it is ACARS equipped.

Thanks for chipping in. I understand the difficulty of identifying who picked the system as an option or not. But the second part of your answer is more what I'm looking for: what would be a reasonable rule of thumb?

@ThxMAD If it's got an electrical system, it can have ACARS. There's definitely 707 and DC-8s with retrofit ACARS. It's actually easier on old planes because they don't have the integrated avionics and displays that modern planes do, they just cut a hole into the console and put a standalone unit in.


text:
Can I overfly Canada on BasicMed?
I’m an FAA PPL using BasicMed. I know Transport Canada doesn’t recognize BasicMed, so I certainly wouldn’t try landing in Canada.
However, can I legally fly from one US airport through Canadian airspace to another US airport, or do I have to go around it?
If it matters, my desired flight would be within the part of southern Ontario controlled by Cleveland Center and Detroit Approach. Does that even count as Canadian airspace?

Well if you're over southern Ontario, yeah you're in Canadian airspace.  It would be Toronto Centre's airspace.

@JohnK Not according to the boundary shown on the IFR Low charts.

@StephenS But it's still Canadian airspace. Which ATC facility is responsible does not change that. Countries often agree to such overlapping ATC responsibilities to simplify things, but they don't give up sovereignty. Where I live e.g., the MUAC controls upper airspace that belongs to Belgium, the Netherlands, Luxembourg and north-west Germany.

Both American and Canadian regulations do not allow you to fly in Canadian Airspace with BasicMed.
Overflights through Canadian airspace with BasicMed are also not allowed, regardless of who controls the airspace.
FAA Regulations

Section 61.113(i)(2)(iii) requires that the flight, including each portion of that flight, is not carried out outside the United States, unless authorized by the country in which the flight is conducted. Title 14 CFR part 1, § 1.1 defines the United States as the States, the District of Columbia, Puerto Rico, and the possessions, including the territorial waters, and the airspace of those areas. Thus, a pilot operating in the United States, as defined in § 1.1, may elect to use BasicMed.
Airmen certificated by the FAA are represented to the International Civil Aviation Organization (ICAO) as compliant with ICAO standards for private pilots, among other requirements. As BasicMed standards divert from ICAO requirements, flights must be geographically limited to operations within the United States, unless specifically authorized by the country in which the flight

Canadian Aviation Regulations

404.03 (1) No person shall exercise or attempt to exercise the privileges of a permit, licence or rating unless the person holds a valid medical certificate of a category that is appropriate for that permit, licence or rating, as specified in section 404.10.

(U.S. recreational pilot certificates and sport pilot certificates are not recognized in Canada)

The same goes for airplane certs in the case of Owner Maintenance category in Can.  I can put most simple single engine aircraft into OM category, which allows the owner who is also the pilot to sign off maintenance releases, do repairs and overhaul, use uncertified parts, etc.  Everything with a serial number has to have an X stamped over the SN and to put it back to Normal Cat you have remanufacture everything.  Problem is OM is not an ICAO recognized category and the FAA refused to give it status similar to amateur built, so an owner can't even overfly US territory in his OM registered 172.


text:
Is a cIearance only valid once it's accepted?
I've read somewhere that "a clearance is not valid until read back correctly," but I can't remember where or find a specific rule saying that.
I understand some clearances can be accepted with "Wilco" or similar in lieu of a full readback, but assume this isn't one of those cases.
For example, is it technically a violation to cross the runway hold bars before you finish reading back a takeoff or crossing clearance?

I know a guy who was busted for blowing through an altitude in a clearance, even though he'd been cleared higher before reaching it, because he blew through the original altitude before he'd read the clearance back.

@JohnK What FAR did they say he violated?

It was in Canada so it would be a CAR (similar).  Not sure exactly.  It's one of those things were 99.9% of the time the controller would let it slide, but if the controller was pissed off at you for something it was something they could do.

I would like to see the controller defend that on appeal.  A total dick move.

Imagine a scenario where you THINK you have been instructed to cross a runway, but the controller actually said something else. While reading back, you proceed to taxi across the runway. The controller doesn't have a chance to stop you, since he can't talk on the radio as long as you are talking.

@J.Hougaard I agree that such a rule would make sense, and for exactly that reason; I just can't find one that actually says it.

Interesting question - although not FAA, I hoped the UK's CAP 413 would hold some insight as it tends to follow ICAO rules:
https://publicapps.caa.co.uk/docs/33/CAP413%20MAY16.2.pdf
Page 25 is the relevant chapter, and while it doesn't outright say the clearance is not valid it is very strong in its readback requirements. The following language applies to runway entry/take off/landing:

The stringency of the read back requirement is directly related to the
  possible seriousness of a misunderstanding in the transmission and
  receipt of ATC clearance and instructions. ATC route clearances shall
  always be read back unless otherwise authorised by the appropriate
  ATS authority
The ATS messages listed below are to be read back in full by the pilot/
  driver. If a readback is not received the pilot/driver will be asked to do
  so. Similarly, the pilot/ driver is expected to request that instructions are
  repeated or clarified if any are not fully understood.
[Lists the relevant activies, including runway entry]

It also points to ICAO Doc 4444:
https://ops.group/blog/wp-content/uploads/2017/03/ICAO-Doc4444-Pans-Atm-16thEdition-2016-OPSGROUP.pdf
With similarly direct wording:

The flight crew shall read back to the air traffic controller safety-related parts of ATC clearances and
  instructions which are transmitted by voice. The following items shall always be read back:
a) ATC route clearances;
b) clearances and instructions to enter, land on, take off from, hold short of, cross, taxi and backtrack on any
  runway; and
c) runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether
  issued by the controller or contained in automatic terminal information service (ATIS) broadcasts, transition
  levels.

It seems clear to me that ICAO, EASA and CAA standpoint is that readbacks are completely mandatory, and the clearance has not been fully delivered until the readback is completed. The readback is a controller final opportunity to correct a potentially critical misunderstanding or communication and it seems to me that proceeding without reading back, and waiting for any call of "Negative" is negligent.

That is clear a readback is required, but it doesn't seem to address whether the clearance is valid before that is complete.

Another question touched this particular topic so I am linking it for your benefit.
When has a pilot legally accepted an ATC clearance or instruction?
The consensus is that the pilot is the PIC (Person In Command) and has the final authority. So there is actually no formal or explicit answer to your question.


text:
How can air stability be predicted?
After several weeks of being grounded due to low clouds, I was looking forward to the cool air, clear skies, high pressure and light winds that arrived this morning as forecasted. However, there is an AIRMET over the whole region for moderate turbulence, so I’m stuck on the ground yet again staring up at a sky that looks like perfect VFR flying weather but somehow isn’t.
The FAA books tell me that turbulence is due to unstable air, but I can’t piece together why it’s unstable today or, more importantly, how I could have predicted it. Which charts or other data should I be looking at, in particular days ahead of time so I know when is best to schedule a flight?

This is a book topic, I don't think there's an answer this. Nations employ whole armies of people with supercomputers to predict the weather, it's not as simple as saying if you look at this chart and that chart you'll know there's turbulence in a couple of days. Looking at your own specific case may be possible if you give the details or where and when.

@GdD The specific case is KADS this morning (11/15/20). Looking at it after the AIRMET came out doesn’t seem terribly useful, but maybe if there’s an obvious cause that I should have seen it coming...

Related

It depends on how far in the future you are trying to predict air stability and turbulence. I am not an expert. But, I would look for some indicators.
For instance, the historic Program Charts from Friday and Saturday show a cold front moving through the area of KADS from West to East. The winds were drastically shifting as the front moved through. This would be an indicator that it might not be a good day to fly. Combine this prognostic data with the METARs from the previous 24 hours to your flight, there is cause for concern for a light aircraft. The winds and gust factors in these METARs might have given you as much as a 24 hour warning of what was to come. Then, there is the Aviation Area Forecast Discussion which will give you further guidance. Lastly (and least used), right before the fight, you could have even checked out the Skew-T/Log-P Diagram in order to judge the strength and severity of the instability.
METARs for KADS:
KADS 141352Z 19008G15KT 8SM BKN009 21/19 A2990
KADS 141447Z 19008G16KT 8SM BKN014 22/19 A2990
KADS 141547Z 19010G25KT 10SM BKN022 24/18 A2989
KADS 141647Z 20017G32KT 10SM BKN028 BKN070 25/18 A2987
KADS 141747Z 19016G31KT 10SM BKN033 27/18 A2983
KADS 141847Z 19016G31KT 10SM BKN039 27/17 A2978
KADS 141953Z 19016G30KT 10SM BKN046 BKN055 27/17 A2974
KADS 142053Z 19012G26KT 10SM BKN050 28/17 A2971
KADS 142153Z 19011G20KT 10SM SCT044 OVC055 27/17 A2972
KADS 142253Z 19016G30KT 10SM SKC 26/17 A2971
KADS 142353Z 19012G21KT 10SM SCT120 26/17 A2973
KADS 150047Z 20009G20KT 10SM SKC 25/17 A2976
KADS 150147Z 20009G20KT 13SM SKC 25/17 A2977
KADS 150215Z AUTO 20009G17KT 10SM CLR 25/18 A2980 RMK AO2 T02450175
KADS 150247Z 18008G16KT 10SM SKC 25/17 A2978
KADS 150255Z AUTO 20009KT 10SM CLR 24/18 A2981 RMK AO2 T02420175
KADS 150315Z AUTO 20008KT 10SM CLR 24/18 A2981 RMK AO2 T02410175
KADS 150335Z AUTO 20009G15KT 10SM CLR 24/18 A2982 RMK AO2 T02410175
KADS 150355Z AUTO 21007KT 190V250 10SM CLR 24/18 A2983 RMK AO2 T02400175
KADS 150415Z AUTO 22004KT 10SM CLR 24/18 A2984 RMK AO2 T02360175
KADS 150435Z AUTO 22004KT 10SM CLR 24/18 A2985 RMK AO2 T02350175
KADS 150455Z AUTO 23006KT 10SM CLR 23/17 A2986 RMK AO2 T02330173
KADS 150515Z AUTO 23006KT 10SM CLR 24/17 A2986 RMK AO2 T02380170
KADS 150535Z AUTO 25007KT 230V290 10SM CLR 24/17 A2987 RMK AO2 T02360169
KADS 150555Z AUTO 29017G23KT 10SM CLR 23/15 A2990 RMK AO2 T02330150 10254 20232 402730182
KADS 150615Z AUTO 33018G24KT 10SM CLR 22/07 A2994 RMK AO2 T02150072
KADS 150635Z AUTO 34020G30KT 10SM CLR 18/02 A2999 RMK AO2 T01820024
KADS 150655Z AUTO 35020G27KT 10SM CLR 17/02 A3002 RMK AO2 T01710015
KADS 150715Z AUTO 35015G22KT 10SM CLR 17/01 A3004 RMK AO2 T01650013
KADS 150735Z AUTO 35013G28KT 10SM CLR 16/01 A3006 RMK AO2 T01610005
KADS 150755Z AUTO 35019G25KT 10SM CLR 16/M02 A3008 RMK AO2 T01571018
KADS 150815Z AUTO 35013G18KT 10SM CLR 15/M03 A3010 RMK AO2 T01541034
KADS 150835Z AUTO 35013G22KT 10SM CLR 15/M04 A3011 RMK AO2 T01501045
KADS 150855Z AUTO 35013G20KT 10SM CLR 15/M05 A3013 RMK AO2 T01461051
KADS 150915Z AUTO 35015G24KT 10SM CLR 14/M06 A3014 RMK AO2 T01441065
KADS 150935Z AUTO 35012G19KT 10SM CLR 14/M07 A3014 RMK AO2 T01391070
KADS 151147Z 35010KT 10SM SKC 12/M07 A3020
KADS 151247Z 35012G17KT 10SM SKC 10/M07 A3022
KADS 151347Z 33005KT 10SM SKC 11/M05 A3025
KADS 151447Z 35012G16KT 10SM SKC 13/M06 A3029
KADS 151547Z 36013G20KT 10SM SKC 14/M07 A3030
KADS 151647Z 02010G20KT 10SM SKC 16/M07 A3032
KADS 151747Z 03010G20KT 10SM SKC 17/M08 A3031
KADS 151847Z 34008G15KT 10SM SKC 18/M08 A3029

Those winds/gusts are not unusual here even when the air is smooth, but the rapid shift in direction was a clue I missed. And I’m wondering now if the instability was due to the ground still being warm right after a cold front moved in, causing thermals even before sunrise? IOW, is that a problem I should expect the day after any cold front?

They may not be unusual. But, it can make landings suck in a light aircraft like a 150 or a SportsCruiser. As far as turbulence, This area is usually good in the morning. And, it gets worse as the day gets warmer. On a clear day, turbulence is to be expected. The clearer the day, the more likely the turbulence. The turbulence and unstable atmosphere actually contribute to clearing the air. On the other hand, hazy conditions or flat, stratus clouds mean a stable atmosphere. The sun heated ground is still heating the air. But, adiabatic cooling is standard and consistent per the skew-t.

@StephenS - P.S. A cold front that is meeting an air mass that is both warmer and moister will have a tendency to push that airmass upwards creating a vertical lifting action similar to a wedge. This may also cause turbulence on an otherwise clear day.

If you edit those comments into your answer, I’ll accept.


text:
What should I do if I intercept the glideslope before reaching the final approach fix?
On several of the ILS and RNAV LPV approaches in my area (and notably the ones I expect for my checkride), I consistently intercept the GS at 0.1-0.2nm before the FAF.
An example: I am flying at exactly 2000 (with correct local altimeter setting) from BONOO to JERIT, but I intercept the GS before reaching JERIT. There are no step-down fixes to worry about.

Should I follow the GS down at intercept, or wait until the FAF and then try to recapture the GS from above? Both seem unwise for different reasons.
I’m looking for a reference sufficient to defend my choice to a DPE.

Doesn't that mean that either the instrument approach isn't setup correctly or your aircraft equipment doesn't work correctly? OTOH, 0.1-0.2 NM isn't that much. How accurately can you measure that?

I wondered if it might be an issue with slant range vs over-the-ground distance measuring (Pythagorean theorem and all). I looked up the distances according to the coordinates given on the 8260-2 form for JERIT and got a hypotenuse of 5.181NM compared to a ground distance of 5.176NM (using Google Earth's claim of 636' elevation at the DME shack, plus a few feet for the antenna). That's a difference of 0.005 DME, so not the answer.

@Bianfable I’m identifying the FAF via GPS (WAAS) substituted for DME. When the display counts down to 0.0nm, I am consistently 1/2 to 1 dot above GS on the HSI.

Technically, there are step down fixes. If you were flying the Localizer (non-Precision) approach and not the ILS, JERIT is a step down fix... From 2000 to whatever the Localizer minimum is for your type aircraft. If flying the Precision, (ILS) then JERIT is really not applicable, the FAF is when you intercept the glide slope at 2000 ft.

@757toga You can delete the comments here that are now redundant with your (accepted) answer.

@757toga Works for me, thanks!

If you are above all the published altitudes for pre-FAF fixes you can intercept the GS but you must remain above the published minimum altitudes as apposed to remaining on glide slope. Approaches may also have defined intercept altitudes for the glide slope. This article explains why quite nicely;

What this means to pilots is that on some approaches, outside the
final approach segment, on a cool day, you might be able to follow the
glide slope and remain above all the published minimum step-down fix
altitudes. However, on hotter than ISA standard days, an aircraft
tracking a glide slope will fly below the minimum altitude for the
published step-down fixes. This could result in loss of separation
between parallel or crossing traffic maintaining assigned altitude by
reference to an altimeter. To avoid a loss of separation, and a
possible pilot deviation filing by ATC, pilots flying an ILS with
step-down fixes prior to the final approach fix must comply with the
minimum step-down altitude, even if it means remaining above the ILS
glide slope until reaching the final approach fix.

and also (bolded for emphasis)

The ILS glide slope is intended to be intercepted at the published
glide slope intercept altitude. This point marks the precision
approach final approach fix (PFAF) and is depicted by the “lightning
bolt” symbol on U.S. government charts or the beginning of the feather
in the profile view on Jeppesen charts. Intercepting the glide slope
at this altitude marks the beginning of the final approach segment and
ensures required obstacle clearance during descent from the glide
slope intercept altitude to the lowest published decision altitude for
the approach. Interception and tracking of the glide slope prior to
the published glide slope interception altitude does not necessarily
ensure that minimum, maximum, and/or mandatory altitudes published for
any preceding fixes will be complied with during the descent. If the
pilot chooses to track the glide slope prior to the glide slope
interception altitude, they remain responsible for complying with
published altitudes for any preceding step-down fixes encountered
during the subsequent descent.

So depending on the scenario you may be able to use the glide slope to help you get an idea of where you are but altitude step downs must be followed prior to the FAF or intercept altitude.

I don’t understand which way you’re telling me to go here. The published altitude at the FAF is 2000, I’m flying at exactly 2000, and yet I intercept the GS before the FAF. Should I follow it down or not?

@StephenS it depends on the situation/approach you can follow it if you are below the GS intercept altitude (if there is a published one) and before the FAF. You can use it as a helper reference so long as you stay above the published step down fixes if no GS intercept altitude is published. In the approach you have here the GS intercept IS the FAF so you can not use it as an official reference prior to the FAF (although this whole approach is only at 2000 prior to the FAF so you could safely fly the GS down prior to the FAF since you are above the min altitude.

@757 the "correct" altimeter setting only provides truly valid information at ground level, right? If the meteorological conditions are other than standard, the pressure lapse rate is different than what the altimeter is calibrated for and it will not match reality. This comment thread on Reddit seems relevant, as does this InFO someone linked.

@randomhead Good point! Maybe it was warmer than ISA and that's why StephenS actually flew a bit higher than 2000 ft and then intercepted the GS a bit earlier.

@Dave Educational about step-down fixes (thanks!), but that doesn’t apply in my example. And your reference is not one I could use on a checkride if the DPE disagrees, as I could with 757toga’s answer.


text:
Why does part 135 require a maintenance log on board the aircraft, but part 91 does not?
During a dispute within friends, it came to my attention that in 135.65 the maintenance log copies must be present in the aircraft, and that 91.407(b) and 91.417(c) have similar rules, but, meanwhile, as indicated in 91.203 the "maintenance logs" are not necessarily maintained and be present in the aircraft. Why is this?
Why didn't a school provide the maintenance logs in the aircraft, but only the airworthiness certificate?
I don't understand the reason behind this; if it must be present in the aircraft for 135 operations (air taxi) why it is not present in 91 operations? Safety wise speaking, I think any pilot who commands a plane, abused by many different people, would want to know what was in the maintenance logs?
I tried to understand the reasoning: maybe the regulators think that it will create another responsibility for PIC? Or maybe this added responsibility will diminish the part 91 owner/operator responsibility? If anybody can explain the underlying rationale for the legislation ıt will be great.

Welcome to aviation.SE! It looks like you have two questions: why are the part 135 and part 91 regulations different? And should pilots expect to see maintenance logs from a school or FBO? Your second question might be answered here; does it help at all?

Part 91 includes Farmer Joe who takes his J-3 around the pattern at his grass strip more often than he takes it out of sight of the farm. Keeping his maintenance log in the hanger makes more sense than stowing it (where?) in the plane. Part 91 rules can be pretty "minimalist" that way, while -135 and -121 are much (much!) more structured.

In Canada you don't keep any maint documentation in the plane, but every a/c has to have a Journey Log where flights are recorded.  You just record date, to/from, air time, flight time, total hours, and make short notations of maintenance competed.  This is separate from the tech logs.  When you purchase an a/c in Canada you have its complete flight history, where it's been, etc.  When you own a homebuilt, as I do, you can actually record all of the maintenance in the Journey Log and aren't legally required to keep tech logs.  I keep copies of Journey Log flight and maint entries at home.

For the same reason truckers are required to keep logs in their trucks noting rest times, inspections, etc. but private vehicle owners do not. Part 135 is for commercial operations, part 91 is not.

Part 135 maintenance log refers to aircraft maintenance discrepancy log, which is a book with

current aircraft times,
travel log with destination codes and Hobbs hours,
airframe landing count and engine cycle count, and
space for a pilot to write a discrepancy, so the mx facility can review and work on the issue and sign it off right in the mx log.

It is a legally bound document needed for part 135 operator because they carry passengers. It is not a whole suitcase with aircraft records (which are actually stored in a facility in fireproof archive cabinets).
You don't need a maintenance log for part 91 privately owned aircraft, unless you want to track all your legs and time, like a flight school does.